Sudan is on the verge of a peace deal ending its devastating 20-year long North-South civil war. But a separate war in the western Darfur region is threatening to not only destroy hopes for peace, but create another African crisis.

Testifying before a U.S. House Subcommittee on Africa Thursday, senior U.S. Agency for International Development official Roger Winter said the problems in Darfur are pushing the Sudanese peace process to the edge of a steep cliff. "Arguably, this is the worst humanitarian emergency in Africa and perhaps in the world at this moment," he said.

The fighting in Darfur, close to Sudan's border with Chad, pits local rebels against government forces and Sudanese-backed Arab militias called the jenjaweed. Mr. Winter says Sudan's Islamic government has been attacking from the air while the jenjaweed loot villages and rape and murder African tribal civilians. He is accusing the Sudanese government of ethnic cleansing.

"You have an African population that is being driven from their homes in a very systematic, widespread and calculated knowledgeable way. If you fly over the locations, you can see the villages burning underneath you," he said.

Mr. Winter denies the Sudanese government's claim that the war in Darfur has ended and that refugees can safely return from Chad. He also says the government has cut off nearly all humanitarian access to the region and takes no action to stop the militias, despte branding them criminals and outlaws.

"When we asked people 'who exactly were these people that did the attacking,' they say 'the janjaweed, the government.' It's the same," he said.

Mr. Winter is calling for an increased effort from the Bush Administration and a robust international presence to protect the people from what he calls a massacre.